There exist several file types that share enc file extension and it is likely that at least some of them can be exported / converted to PDF format. For example music notations from Encore (.enc) may be possibly exported as PDF documents.
Also, some .enc files are known to be generated (encrypted and renamed) by some ransomware. In this case, you would need to first decrypt the file with some kind of decrypter and then you may convert the original content. Sadly, not every ransomware can be decrypted.